The present invention relates generally to an apparatus and method of removing unnecessary matter on an edge portion of a substrate or other workpiece, such as a semiconductor wafer or a liquid crystal display device. Particularly, the present invention relates to an apparatus and method suitable for removing the thick raised part of coating on a substrate about its edge portion (i.e., the portion at the outer perimeter of the substrate) when the coating has been applied through, for example, a conventional spin coating process. The present invention also relates to a spin coating process which includes using a method of removing the thick raised unnecessary matter at the edge portion of the substrate.
According to methods well known in the prior art, an insulation or mask layer may be formed on a substrate by spin coating a liquid glass material (SOG: Spin On Glass), organic resist, polyimide or the like on a substrate or other workpiece, such as a semiconductor wafer or liquid crystal display device. Further, a thin film may also be formed on the substrate of a liquid crystal panel through a spin coating process. In the spin coating process, the substrate is rotated about an axis orthogonal to the surface to be coated and the coating material is applied on the surface at a point near the axis of rotation. The coating is spread out over the middle area of the substrate into a substantially uniform thickness from the centrifugal force driving it away from the point near the axis of rotation and towards the perimeter edge portion.
However, these prior art spin coating processes have the disadvantage that the coating formed on the edge portion of the substrate tends to have a greater thickness than the coating at the middle area thereof, and thus forms a thick raised part containing unnecessary matter on the edge portion of the substrate or other workpiece.
If a coated semiconductor wafer or liquid crystal panel formed from the spin coating process is then utilized as a workpiece for some other operation device, for example, if the substrate is conveyed by a conveyor or housed in a transportation cassette, or placed on a stage in an ion-implantation device or dry-etching device, the raised part on the edge portion of the substrate may easily be fractured and create dust. Such dust may deposit on the substrate causing contamination or may cause contamination of the operation device. This raises the problem of the yield being greatly reduced for the semiconductor production.
In order to remove this unnecessary raised part of coating about the edge portion of the substrate which typically forms during the spin coating process, it has been previously proposed that after the spin coating step is performed, a series of photolithographic steps be carried out. These photolithographic steps include a resist coating step, an edge exposing step, a developing and baking step, a wet-etching step and a resist removing step. Since these photolithographic steps may require a prolonged time (e.g., on the order of one to three hours), the efficiency of production of finished semiconductor wafers or liquid crystal panels is undesirably reduced.
Depending on the product to be formed, the resist removing step can occur simultaneously with the other mask forming and etching steps which may already be used in the procedure of manufacturing the semiconductor wafer or liquid crystal display panel. Since the raised part of the coating still exists on the edge portion of the substrate prior to the mask forming and etching steps, however, the reduction of yield due to creation of dust which contaminates the finished product can not be avoided.
Japanese Patent Laid-Open No. Hei 5-82478 discloses a method and apparatus for etching the end faces of a semiconductor wafer by using atmospheric plasma The method described therein includes grasping the middle area of the semiconductor wafer between upper and lower disc-like holders in a circumferential reaction chamber and exposing the semiconductor wafer only at its edge portion thereof to an atmospheric plasma treatment. The outermost peripheries of the upper and lower disc-like holders carry an O-ring packing at their circumference which not only may grasp the semiconductor wafer, but also may form an air-tight seal separating the middle area of the semiconductor wafer from the raised edge portion of the semiconductor wafer.
The technique described therein requires bringing the O-rings into firm contact with the middle area of the semiconductor wafer. However, often in the middle area of the semiconductor wafer, active elements and electronic components are formed. Thus, these surface structures, such as the active elements and electronic components, may be damaged by the pressure exerted by the O-rings. Additionally, dust may yet continue to be deposited on the middle area of the semiconductor wafer, thus degrading the efficiency of production.